I installed Ubuntu 12.04 on my external USB drive, where I have a 700GB NTFS partition followed by the new 6GB ext4 partition and a swap partition (all primary). The GRUB MBR is also installed to the external hard disk.

Since my BIOS puts the external drive as first disk when booting, I removed my internal hard disk before installation in order to avoid ordering problems.

Now when I boot from the external drive, GRUB is stuck at the rescue console with the error "unknown filesystem".

Yes, when I start from the live CD, the internal is /dev/sda and external is /dev/sdb. But when I boot from the external, my bios sets the USB drive as the first disk. That's why I installed with my internal hard drive unplugged. But even if I install Ubuntu with that drive plugged in, same issue...
–
AndiDogMay 6 '12 at 21:45

4 Answers
4

OK, is sda your hard drive and sdb the USB?? Thank you for your reply. I've suggested this to a lot of people and that is to burn a CD of SuperGrub Boot Disc. You boot from that and it will present you with a list of OSs to choose from. Try that next. Following that, what happens if you try to examine the contents of those partitions from a Live CD install?? Are they readable now??

I have had this same problem, I have tried most suggestions found here and in other well answered post with no success.

I kind of found a simpler way of fixing it, and just wanted to share this newfound knowledge with you all, who are as I was trying to solve it in a too complicated way.

So, my NTFS storage partition was almost 2 Tb, which is too big for the ext filesystems if I am correct. There is software to actually move a partition, with all its data, to the back of the drive. Thus you can split it, move the stored data, and create a new partition with ext3 or ext4, or your system of choice, in the beginning of the drive. This made Ubuntu directly bootable without hassle.

I used Minitool Partition Wizard Home edition. And I can assure you, that data is moved, and not wiped. I don't know if gparted moves the data as well?

My USB drive has first NTFS partition of 430GB (sdg1) followed by Linux partition of 10 GB (sdg2) (all primary).
I installed Ubuntu (or afterwards Trisquel) to it and had the same error about unknown filesystem.

It was that grub was unable to "see" Linux partition after such "large" NTFS partition. I don't know the exact limitations of GRUB2, but my 430GB was above it.

Here is the workaround:

Install grub to USB HDD with root directory at /dev/sdg1 (NTFS partition). You then will have grub.cfg in /boot/grub/ on that partition.

Copy kernel and inirtd image to /boot/ubuntu/ at /dev/sdg1.

Change grub.cfg to have root at 'hd0,msdos1' and to load kernel and initrd from /boot/ubuntu/.